Method and apparatus for continuous coating of endless metal bands with synthetic resins



Aug. 9, 1966 Filed April 1 1963 LICHTE METHOD AND APPARATUS FORCONTINUOUS GOATING OF ENDLESS METAL BANDS WITH SYNTHETIC RESINS 2Sheets-Sheet 1 Aug. 9, 1966 A, LlcHTE METHOD AND APPARATUS FORCONTINUOUS COATING OF ENDLESS METAL BANDS WITH SYNTHETIC RESINS 2Sheets--Shee'c 2 Filed April 1, 1963 Ffg z Fig 3vllllllll..lllllillrlfrlvlrrllf United States Patent O 3,265,525 METHODAND APPARATUS FOR CONTINUOUS COATIN G OF ENDLESS METAL BANDS WITHSYNTHETIC RESINS Albert Lichte, Wuppertal-Elberfeld, Germany, assignorto Schloemann Aktiengesellschaft, Dusseldorf, Germany,

a German company Filed Apr. 1, 1963, Ser. No. 269,394 Claims priority,application Germany, Apr. 4, 1962, Sch 31,252 4 Claims. (Cl. 117-49)This invention relates to a method of and apparatus for the bubble-freecoating of thin layers of synthetic material, in a liquid or pastycondition, in a continuous operation, upon continuously accuring endlessmetal bands, and for the rapid hardening of the layer of syntheticmaterial so applied.

The synthetic coating material may consist of mixed PVC polymerizates,acrylic resins, alkyds, or certain proprietary preparations of the kindcommonly known as plastic lacquers.

The object of the invention is to carry out the coating and hardening ina small space, with simple apparatus and small operative expenditure, inas short a time as possible. In particular, the drying or gelatinisingand hardening times are to be short, and a rapid change-over todifferent materials and orders of magnitude, with dustfree working, isto be rendered possible.

The invention consists in applying the synthetic material, which hasbeen brought into a pasty to liquid condition by means of a solvent ofthe ketone group for example, to the band to be coated, in a vacuum, andeiecting the hardening or polymerisation of the applied layer in avacuum, or at least in a treatment chamber at a lowered pressure. (Whenreference is hereinafter made to vacuum, what is meant is a loweredpressure which is less than atmospheric pressure). Owing to the factthat in a vacuum the fractional distillation of the solvent can bereduced by lowering the boiling points of the participating solvents,the gelatinisiug, drying or polymerising process, which is controlled bythe solvents, admits of being considerably shortened.v The usualsolvents, for instance methyl ethyl ketone, evaporate in a normalatmosphere at about 80 C. By adopting a slightly lowered pressure,between 100 and 40 Torr (.millimetres of mercury) for example, theboiling point can be shifted to room temperature or lower. This has theadvantage that following the vaporisation of the solvents a cooling ofthe coated band in the conventional sense is no longer required. Theentire drying tract for the hardening of the coating is therebyconsiderably shortened, so that a considerable increase in the speed ofpassage of the band is possible. Besides the advantages of a greatercoating output, the coating materials applied in a vacuum are free frombubbles and free from dust. Additional advantages are yielded by thevacuum treatment, in that the solvent vapours arising from thevaporisation of the solvents can be condensed by appropriate coolingdevices and collected. The consumption of solvents can thereby beconsiderably reduced. Furthermore, in the coating of light metals,aluminium bands for example, there is an advantage, in that noalteration in the technological properties of the aluminium band isbrought about, because the drying in a vacuum is eifected below therecrystallisation temperature.

Finally, as compared with conventional coating installations, asubstantially smaller consumption of energy is also an advantage, for`only the heat of vaporisation eliminated in the evaporation of thesolvents need be resupplied. This supply of heat, which is in any casenecessary for the maintenance of the vaporisation temperature,

is however comparatively small.

3,265,525 Patented August 9, 1966 ICC The apparatus for carrying out theprocess according to the invention, which comprises a vacuum chamberserving for the vacuum treatment, closed in an airtight manner, at boththe band-admission and the band-exit ends, in a known manner by vesselscontaining liquid, is characterised by the feature that at the samelevel as the sealing-'liquid containers, and between these, treatmentvessels are provided, and that the sealing-liquid vessels are in eachcase connected by way of one connecting tube, but the treatment vesselsin each case by way of two connecting tubes, with a vacuum tank arrangedabove at a higher level, in such `a way that the band to be coated canbe carried through the apparatus in a number of vertical loops, thereversing rollers that carry the band, and also the Vactual coatingappliances, being arranged partly in the sealing and treatment vesselsand partly in the vacuum tank.

The installation costs of this apparatus, as compared with conventionalplants, are extremely low. The vacuum chamber, having regard to thepurpose for which it is employed, is by this arrangement kept verysmall, and owing to the vertical tube lconnection of the liquid vesselswith the upper vacuum tank, the provision of as high a Vacuum as may bedesired is possible, since the column of liquid sucked up by the vacuumin these connecting tubes can be raised as far as may be wished.Independently of the height of the vacuum, therefore, a constantlycontinuous passage of the band through the apparatus is given. Thesealing-liquid baths may at the same time serve as treatment baths, forinstance in such a manner that the liquid seal at the band-admission endof the apparatus constitutes at the same time the last cleaning stage ofa preparatory treatment of the band, whilst by the liquid seal at theband exit end an after-treatment of the finished band may at the sametime take place, for instance in such a manner that the coated band ishere coated With a thin protective lm, in order to prevent anelectrostatic charging, and therefore an attraction of dust.

These and further details of the process according to the invention, aswell as of the apparatus according to the invention, are furtherexplained by reference to a constructional example, which is illustratedin the `accompanying drawings, in which z' FIGURE 1 shows in frontelevation theA apparatus according to the invention;

FIGURE 2 is a diagrammatic representation of a coating `appliance knownin itself;

FIGURE 3 shows a section on the line III--III in FIGURE 1; yand FIGURE 4a section on the line IV-IV -in FIGURE 3.

The apparatus illustrated consists essentially of four vessels 1, 2, 3,4, erected side by side in one plane, a vacuum tank 5 arranged above4them at a higher level, and six vertically extending connecting tubes6, 7, 8, 9, 10, 11, by which the lower vessels 1, 2, 3, 4 are connectedwith the vacuum tank 5. In order to ensure a satisfactory sealing, thatis, a vacuum-tight sealing, of the connecting tubes 6, 7, 8, 9, 10, 11,each of the lower vessels 1, 2, 3, 4, is equipped with two upwardlydirected tubular members or sockets 1a, 1b, 2a, 2b, 3a, 3b, 4a and 4b,whilst the vacuum tank 5 above them has six downwardly directed sockets,c, d, e, f, g and h. The connection of the lower vessels 1, 2, 3, and 4with the upper vacuum tank 5 is here established by means of theconnecting tubes 6, 7, 8, 9, 10 and 11 in such a way that the band 12 tobe coated can be passed through the apparatus in a succession ofvertical loops by way of lower reversing rollers 13, 14, 15, 16 arrangedinside the vessels 1, 2, 3 and 4, and by way of upper reversing rollers17, 18, 19 journalled in the vacuum tank 5. The open socket 1a of thevessel 1 here serves as an entry into the apparatus, and `the socket 4aof the vessel 4 as an exit from the apparatus. The band admission roller20, and

the band outlet roller 21, are located at about the same level outsidethe apparatus itself.

All parts of the apparatus, that is, the lower vessels, the vacuum tankand. the connecting tubes, may fundamentally be made of any Idesiredcross section, even square or rectangular. A round or at least ovalcross-sectional form is however preferred. The production of the vacuumis eected by vacuum-producers not represented in the drawings, such forinstance as pumps, steam-jet ejectors, condensers or the like, which areconnected to the upper vacuum tank 5 by way of tank unions 22.

The vessels 1 and 4 both serve -as liquid-containers for theaccommodation of sealing liquid, and thus are at the same time sluicesfor the air-free admission and exit of the band. The sealing medium isin both cases an aqueous solution. The solution in the vessel 1, thatis, at the end at which the band enters, may also pertain to the lastcleaning stage of the preparatory treatment of the band. The solution inthe vessel 4, on the other hand, may be a special solution, which, asthe coated band runs through, deposits upon the surface of the band aprotective film, by which an electrostatic charging, and therefore anattraction of dust, is prevented.

During the operation, in dependence upon the height of the vacuum in theapparatus, the solutions in the vessels 1 and 4 are drawn upwards bysuction linto the vaeuum space, that is, into the connecting tubes 6 and11. In each of these connecting tubes 6 and 11 a column of liquidcorresponding to the vacuum accordingly adjusts itself. On the vessels 1and 4 are also provided overflow spouts 23 and 24, by which thesolutions in these Vessels tlow away into a collecting receptaclelocated lower down and not represented in the drawing, to be pumped backagain from there into the vessels by way of the sockets or pipecouplings 1a and 4a, which are open to the atmosphere. This has theadvantage that the surface level of liquid in the vessels 1 and 4 alwaysmaintains a constant height, even if accidental iiuctuations shouldoccur in the vacuum. Furthermore in this way the composition of theSolution can be constantly checked, and can be supplemented or renewedin case of need.

The vessels 2 and 3 serve as treatment vessels, and are subject tovacuum. They contain, besides the lower band-reversing rollers 14 and 15respectively, the actual coating devices 26 and 28 respectively, forapplying an adhesion-promoting medium and the layer of syntheticmaterial respectively. Similar :coating devices 25 and 27 are moreoverprovided in the vacuum tank 5, the coating device 25 being designed forapplying an adhesion-promoting medium and the coating device 27 forapplying the layer of synthetic material. The adhesion promoting mediummay be the proprietary preparation known as mesamol, or some similarprimer.

Each coating device, as shown in FIGURE 2, consists of a trough 40containing the liquid synthetic material or the adhesion-promotingmeans, a dipping roller 41 dipping into the trough, and an applyingroller 42 co-operating with the dipping roller. The entire unit,including its drive, is supported in the vacuum space, and each suchunit is arranged in the neighbourhood of one of the reversing rollers14, 15, 17 or 13 that guide the band 12, so that during the applicationof the layer of synthetic material the reversing roller serves as acounter-pressure roller.r

In order to enable the thickness Vof the coating to be accuratelyadjusted while it is being applied, the entire coating :device isdisplaceable towards the band, that is, towards the centre of thereversing roller. The troughs 40 containing the liquid syntheticmaterial have each an overow connection as well as an inlet connection.These connections are in communication with a storage vessel, which isarranged outside and underneath the vacuum plant. In order that thecoating materials may not dry up, and that their viscosity may bemaintained, they are -continuously pumped round. For the maintenance ofthe vacuum it is however requisite that the connecting pipes should forma U-shaped loop extending vertically downwards and corresponding to ltheheight of the Vacuum, s0 as to counteract the suction produced by thevacuum.

The bottoms of the treatment vessels 2 and 3 are so constructed that ina method of working with a rather coarse vacuum `of for instance morethan Torr, the solvent condensing on and running down the cooler wallsof the tubes 7, 8, 9 and 10 can be caught underneath. By specialdischarge pipes 29 and 30 the condensate is drawn olf, and the surfacelevel of the condensate in the vessels 2 and 3 is maintained constant.The discharge pipes 29 and 30, like the connecting tubes of the coatingdevices, are of U-shaped construction and extend vertically downwards,the length of the U-shaped loop having to be adapted to the height ofthe vacuum. For the satisfactory condensation of the vaporised solvent,cooling devices, for instance cooling coils 31, may if desired beprovided in the ltreatment vessels 2 and 3. An external cooling of thevessels 2 and 3, or of the connecting tubes 7, 8, 9 and 10, is howeverlikewise possible.

The treatment or coating of the band 12 is effected in the treatmentvessels 2 and 3 and in the vacuum tank S. The connecting tubes 6 and 11serve as drying spaces for the drying and hardening of the coatingmaterial, so that the length of the drying Atract is determined by thelength of the connecting tubes. By increasing the length of theconnecting tubes, therefore, the length of the drying tract can beincreased in `a very -cheap and simple manner, with out the otherstructural parts of the apparatus having to be altered. The connectingtubes 6 and 11 communicating with the liquid vessels 1 and 4 serve atthe same time as stand-pipes for the columns of sealing liquid suckedupwards by the vacuum.

In order to accelerate the drying and handening or polymerisation of thefreshly applied coating, and at the same time to make good the heatremoved by vaporisation of the solvents, heating devices 32 areinstalled in the connecting tubes. Since the transfer of heat in thevacuum can only be effected by radiation, the heating devices 32 arepreferably infra-red radiators or similar thermal radiators. Theseheating devices are located near the band surface just coated, and areso arranged that an intensive irradiating o'f the coating substances ispossible.

One form of construction, by way of example, of a heating applianceconstructed as a thermal madiator, is shown by FIGURES 3 and 4. Thethermal radiator elements are lassembled into Ignoups, each -gr-oup ofradiators consisting lof a number of tubes 34 arranged transversely tothe direction in which the band passes, and welded in a vacuum-tightmanner to the connect-ing tube, for instance to the `t-ube 7 in FIGURES3 and 4. The thermal radiating tubes 34 yare `open at both ends, so thatany desired source yof heat can be fitted in or connected thereto. Forthe strengthening and intensifying orf the yradi-ating eiIect,reflectors 3S are provided on the side of the thermal radiating tubes 34remote from the band 12, as shown in FIGURE 4.

If the connecting tubes 7 to 10 are provided throughout their lengthwith such radiating tubes 34, they admit of being used Ioptionally forheating or for cooling. In this way the entire apparatus can be widelyadapted to all coating requirements.

The working procedure or coating paratus according to the invention isas follows: T-he band 12 to be coated is introduced, by way of thebandentry 4roller 20, through the open tubular member la, into theliquid vessel 1, and is guided upwards by the reversing roller 13,journalled in the liquid, 'into the connecting tube 6. In` the upperpart ofthe connecting tube 6 is mounted a heating device 32, whichvaporises drops of water that operation in the aphave remained clingingby adhesion to the surface of the band. Upon the deflection of the band12 round the upper reversing roller 17, an adhesion-promoting medium isapplied to one side off the band by the coating device 25. Upon thefurther tr-avel of the band this applied layer is irradiated by theheating device 32 located in the connecting tube 7, the solventevaporating and the coating itself being dried out. In the treatmentvessel 2, by means of the coating device 26, the other side ofthe bandis then provided with an adhesion-promoting medium, which, upon the bandascending again, is dried in the connecting tube 8. As the band passesround the upper deflecting roller 18, lthe first side of the band is nowcoa-ted with a synthetic material, which, during the further travelthrough the connecting tube 9, is hardened or polymerised by the aid ofthe heating device 32 therein. Then in the treatment vessel 3 thecoating of the second side of the band with synthetic material iseffected as it passes round the delecting roller 15, the hardening orpolymerisation being eifected in the succeeding connecting tube 10. Bythe upper deflecting roller .19 the band 12 is deflected downwardsagain, and dips, in the connecting tube 11, into the liquid seal of theliquid-container 4. After deflection of the band by the lower reversingroller 16, journalled in the liquid container 4, the band then leavesthe apparatus through the open tubular member 4a to be guided away overthe band exit roller 21.

Immediately before the coating appliances 27, 28 that apply the coatingof synthetic material, further heat-radiating devices m-ay be Iprovided,for the purpose :of transiently softening by heat the adhesion-promotingcoating already applied. A bet-ter adhesion of the layer of syntheticmaterial can be obtained in this way, according to the consistency ofthe coating substances.

I claim:

1. Apparatus for applying thin synthe-tic coatings to metal bands andhardening the coatings, comprising: a closed liquid container formedwithan inlet for the band to be coated, a closed liquid container formedwith an outlet for the coated band, treatment vessels located betweenthe two liquid containers and at the same level, a vacuum tank locatedabove the liquid containers and treatment vessels, a connecting tubeextending upwards from each liquid container to the vacuum tank, twoconnecting tubes extending upwards from each treatment vessel to thevacuum tank, reversing rollers so a-rranged in the liquid contaliners,treatment vessels and vacuum tank that a band entering the first liquidcontainer through the band inlet can pass round the reversing rollersand through the liquid containers, treatment vessels, vacuum tank andconnecting tubes in a plurality of vertical loops to the band outlet,means ttor exhausting air from the vacuum tank,

the treatment vessels and the tubes connecting them w-ith one another,means in the treatment vessels for -applying a solution of syntheticcoating material in an atleast semiliquid condition to that side of theband tha-t does not come into contact with the rollers therein, means inthe vacuum tank for applying synthetic coating material in an at semi-Iliquid condition to that side of the band that does not come intocontact with the reversing nollers in the vacuum tank, and means in theconnecting tubes .for heating that side of the band which in each caseyhad not come into contact with the preceding reversing roller.

2. Apparatus for aplyin g thin synthetic coatings to metal bands `andhardening the coatings as claimed in claim 1, the heating means in theconnecting tubes being infra-red radiators.

3. Apparatus for applying thin synthe-tic coatings to metal bands andhardening the coatings as claimed in claim 1, funther comprising:cooling means for condensing the vapours of the solvent removed from thesynthetic coating by the heating means, and discharged pipes forremoving excess condensed solvent from the treatment vessels withoutdisturbing the vacuum therein.

4. A method for the bubble-free application of thin coatings of:synthetic material, in a continuous operation, to -a continuouslyadvancing metal band, and for the rapid hardening of the coatingsapplied, comprising: bringing the synthetic material into an at leastsemi-liquid condition by means of a solvent, applying this semi-liquidmaterial to the band ina partial vacuum, hardening or polymerizing thecoating so applied, still in a partial vacuum,

- the height of the vacuum being such that the vaporization temperatureof the solvent is at about room temperature, and replacing the heat ofvaporization, which is withdrawn from the synthetic material in thevaporization of the solvent, by thermal radiation from an externalsource.

References Cited by the Examiner UNITED STATES PATENTS 987,629 3/191'1Ketchson 117-61 X 1,069,033 7/1913 Rowland 118-61 1,322,327 11/1919Minton. 1,331,729 2/1920 Taylor 117-61 1,595,236 8/1926 Minton 117-611,595,475 8/ 1926 Minton 117-61 2,137,256 11/ 193 8 Waldron 117-6-1 X2,346,523 4/ 1944 Vincent 117-61 2,894,483 7/1959 Stahl 118-50 2,937,1085/1960 Toye 117-119 X MURRAY KATZ, Primary Examiner.

JOSEPH B. SPENCER, Examiner.

1. APPARATUS FOR APPLYING THIN SYNTHETIC COATINGS TO METAL BANDS ANDHARDENING THE COATINGS, COMPRISING: A CLOSED LIQUID CONTAINER FORMEDWITH AN INLET FOR THE BAND TO BE COATED, A CLOSED LIQUID CONTAINERFORMED WITH AN OUTLET FOR THE COATED TREATMENT VESSELS LOCATED BETWEENTHE TWO LIQUID CONTAINERS AND THE SAME LEVEL, A VACUUM TANK LOCATEDABOVE THE LIQUID CONTAINERS AND TREATMENT VESSELS, A CONNECTING TUBEEXTENDING UPWARDS FROM EACH LIQUID CONTAINER TO THE VACUUM TANK, TWOCONNECTING TUBES EXTENDING UPWARDS FROM EACH TREATMENT VESSEL TO THEVACUUM TANK, REVERSING ROLLERS SO ARRANGED IN THE LIQUID CONTAINERS,TREATMENT, VESSELS AND VACUUM TANK THAT A BAND ENTERING THE FIRST LIQUIDCONTAINER THROUGH THE BAND INLET CAN PASS ROUND THE REVERSING ROLLERSAND THROUGH THE LIQUID CONTANERS, TREATMENT VESSELS, VACUUM TANK ANDCON-